Tool for stringing tennis rackets



y 4, 1944- B. F. MIESSNER 2,352,730

' TOOL FOR STRINGING TENNIS RACKETS Filed March 31, 1943 2 Sheets-Sheet 1 IN VEN TOR.

BENJAMIN EM/ESS/VER f7 TTORNEY July 4; 1944. s. F. MlE SSNER 2,352,730

TOOL FOR STRINGING TENNIS RACKETS Filed March 31, 1943 2 Sheets-Sheet 2 INVENTOR. 5E/VJ/7/Wl/V FM/ESS/VER Patented July 4, 1944 UNITED STATES PATENT OFFICE 2,352,730 TOOL FOR STRING-ING TENN IS RACKETS Benjamin F. Miessner, Morristown, N. J.

Application March 31, 1943, Serial No. 481,257

4 Claims.

The invention relates to tools for use in stringing tennis rackets, and has for its object to provide a novel tool of the indicated class whereby the string tension may be measured so that equal tension, or any other desired ratio of tensions, may be obtained with accuracy in the various strings of a given racket.

Another object of the invention is to provide a novel tool whereby the generally accepted technique of ra'cket stringing involving the use of a dowel may be efliciently utilized. 4 The invention contemplates-further the provision of a novel tool with which the strings may be frictionally ngaged in a simple manner to revent slippage.-

In addition, the invention. proposes to provide a novel tool including a handle capable of being easily gripped in an efiective manner.

Still another object of the invention is to provide a novel tool which embodies the aforesaid objects and whichis compact, inexpensive and of maximum durability.

In stringing a tennis racket frame tensions of the order of fifty or sixty pounds are customarily used. According to existing practice, this tension is applied by looping the string several times around a dowel which may consist of a six or eight inch length of old tennis racket handle. The string is also wound over itself to prevent slippage and, after this operation, the dowel is close to the racket frame and at right angles to its plane.

The dowel is then manually rotated aboutits major axis, in increasing pressure contact With the racket frame, until the tension in the given string appears correct, whereupon a sharplypointed awl or equivalent instrument is forced into the string'hole'adjacent the string to clamp the latter under tension. This prevents slippage of the tensioned string while the free portion of said string is unwrapped from the dowel; then said free portion of the string is threaded through the next hole, again wrapped around the dowel and the tensioning operation repeated. These operative-steps are repeated until the racket has been fully strung.

Injudging the tensionthe stringer watches the tautness of the string and its stretch; he also, for thefirst set of parallel strings, plucks them with his-finger and listens-to the pitch of their sounds. The purpose is always to obtain uniform tension for all of-thestrings so that:

.(1)- The. various strings will all-contribute equally to the resiliency of the ball-striking -surface; V.

(2) So as to prevent undue wear on the more highly tensioned strings accompanying unequal tension;

(3) So as prevent an undesired rolling tendency of the ball on the racket strings;

(4) So as to prevent twisting of the-racket handle in the player's hand under impact of the tennis ball on said strings, and

(5) In general, to provide amore uniformlyacting racket, and a longer-lived and more resilient stringing. r

Heretofore, arrangements have been provided for attainment of equal tension stringing, but these have been expensive, complicated, and too involved in operation for practical useas a re suit the very simple method, above described, has been generally used. This method, however, yields a very low order of accuracy in tension adjustment for the following reasons;

(1) Judging the tension by; the appearance of tautness is extremely inaccurate and wireliable; I

(2) Judging the tension by apparent stretch of the string is also very unreliable;

(3) Plucking the strings and listening to their audible tone may be an accurate method of measure tension in equal length strings, but without pitch standards for comparison this is also very unsatisfactory for these reasons:

(a) It can only. be used on the first set of parallel strings, since, because of interweaving the second or cross set of strings are prevented from freely vibrating by the first set.

(D) Thetest can be used to insure like tension in the equal length strings of the first set if the correct. pitch for the desired tension is known, but, since the length ratio. of the shortest to the longest strings in this set is about one to two, tensioning .of all these strings'to the same pitch, ascommonly practiced, results in widely differing tensions in the difierent strings. If the pitches of the shorter strings are made-progressively higher than the longer ones the tensions will in some degree be equalized but without proper comparison pit'ch standards, equal tension is only very roughly accomplished.

For a given material the frequency of string vibrations (neglecting a small correction due to inherent stiffness) is directly proportioned to the square root of the tension, inversely proportioned to thesquare root of the mass per unit, length, andinversely proportioned to the tension, thus ..It.is seenhere that two strings of the same material, one, twice the I length ofthe other.

would have one-half the frequency of the other.

If these two strings are tensioned to the same pitch, the longer one will have four times the tension of the shorter one.

The vibration frequency varies inversely as the square of the mass per unit length. This involves both the string diameter and the material, such as gut, silk or nylon, so that variations in diameter and material of the string introduce other factors which materially influence the pitch test for correct tension.

Under the circumstances, practical racket stringers, who relay upon the pitch test, can hardly be expected to attain the desired uniform string tension.

The stringing tool of the present invention overcomes the above conditions and objections and directly measures the tension of each string by an internal tension measuring device as will be clearly pointed out hereinafter.

Other objects will. appear from the description hereinafter and the-features of novelty will be pointed out in the claims.

In the accompanying drawings, which illustrate anexample of the invention without defining its limits;

Fig. 1 is an elevation of the novel tool;

Fig. 2 is a longitudinal section thereof on the line 2 2 of Fig. 1; Fig. 3 .is an end view ofthe novel tool;

Fig. 4 is an enlarged fragmentary section illustrating a grooved sheave and associated parts included in the tool;

Fig. 5 is a detail face view of a head forming part of-the tool;

Fig. .6 is a section thereof onthe line 6-6 of Fig. 5;.

Figs. 7 and 8 are face views of the sheave showing two different types of tension scales embodied in the novel tool;

Fig. 9 is a plan view of a tennis racket showing the novel tool in use;

' Fig. 10 is a side elevation thereof, and

Figs. 11 and -12.are detail views illustrating the tool in use upon opposite sides of the racket frame,v

. As shown in Figs. 1 and 2, the novel tool comprises a handle I15 of wood or other suitable material preferably provided with a covering |6 of leather or the like secured in place in an convenient manner as by gluing or the like. A rod or shaft H, preferably of steel or other metal, extends lengthwise .of the handle 15 interiorly thereof in registry with the longitudinal axis thereof and projects beyond one end of said handle l5 as shown in Fig. 2. The. rod or shaft l! is fixed against rotation and other movement relatively to the handle [5 in any convenient manner as by means of a pin It or the like.

. Asleeve or tube I9 is mounted upon the projecting end of the rod or shaft I! and preferably extends into an axial bore with which the handle I5 is provided for the purpose to be more fully set forth hereinafter. The sleeve or tube I9 is rotatable upon the rod or shaft and exteriorly of the handle l5 carries a peripherallygrooved sheave 2| fastened on said tube l9 in any conventional manner as by being soldered thereto. The peripheral groove 22 of the sheave 2| preferably is of V-shape or equivalent form in cross-section as shown in Figs. 1 and 2.

.A torsion spring .23 of, helical or other suitable form is located within the bore 20 and surrounds the rod or shaft H with its innerv end suitably secured thereto and its outer end solderedor 1-5 otherwise attached to the sleeve or tube l9 on the sheave 2| and preferably also to the latter, for instance, as shown at 23a and 23b in Fig. 4.

A head 24 preferably of circular form is fixed upon the outer end of the rod or shaft I"! in any suitable way. Preferabl the head 24 is of recessed form including a peripheral flange 25 and an internal central hub 26 provided with a rectangular or other non-circular opening 21 which fits over the rectangular .or other corresponding non-circular end 28 of said shaft or rod against an annular shoulder 29 thereof formed at the base of the relatively reduced end 28 as illustrated in Fig. 2. The head 24 may be secured in placeon said rod or shaft I! as by means of a set screw 30 which is threaded into said rod or shaft l1 and bears against the hub 26. The arrangement is such that the annular shoulder 29 prevents the head 26 from binding the sheave 2| against relative rotative movement.

The clearance between the sheave 2| and the head 24 on the one side, and the end of the handle I5 on the other, is small enough to prevent the racket string from slipping between these parts when the tool is in use and at the same time is sufficient to permit free rotation of said sheave 2|.

In the preferred construction the head 24 is made of metal, and metal ,band 3| is provided on the handle l5 adjacent the .sheave 2| and fixed in place in any convenient manner. This band 3| being located at the point of contact between the tool. and the racket frame, when the novel tool is in use, serves to prevent undue wear.

The novel tool further includes means for visibly indicating the tension .appliedto the strings by said tool. 1

In the illustrated example, the means in question comprises tension scales 32 consisting of figures representing pounds for other predetermined units of measurement. The figures of the scales 32 are located on the one face of' the sheave 2-| and are visible in succession through an index opening or window 33 provided in the bottom of the head 24. The figures of thescales 32 may be produced directly -on said face of the sheave 2| in any convenient manner, or said scale figures may be printed on paper, metal or other suit-able'material which is attached to the sheave 21 by cement or other adhesive or by rivets or equivalent fastening means.

When tension is applied tangent to the sheave 2|, as by a racket string, .a torsional force is developed which is opposed by the torsionaltension of the spring 23. The angular displacement of the sheave 2| is .thereforea measure of the string tension. The radius arm of this tension force, developing torsional .force on said sheave 2| is maintained relatively constant due to the shallow depth of the V-groove 22, and by the operating technique by whicl-rone and one-halfto two turns of string are always used around .said V- groove 22. Y.

For some strings the novel tool-must be twisted rotatively in a clockwise direction as illustrated in Fig. 12 while for 39111181 strings it must :be rotatively twisted acounter-c-lockwise direction as shownin Fig. 1.1. This is evident when it is noted that some strings extend across the racket frame from left :to. right .whileoth-ersextend fromright to left.

Since the tension therefore must .bermeasured for 'both clockwise and icountereclocltvfise manila ulation of the tool, its torsion spring 23 andtension scales 32 tions.

A single :spring 23 ;may-. operate; satisfactorily for both directions, or a doubly-wound spring construction maybe used, wherein the spring is wound from one end to the othenand then back over the first winding to-thestarting point.

The tension scales 32 may havetwo sets of tension figures, for instance, from. 012070 pounds, one increasing. clockwise and the other: counterclockwise as illustratedinFig. '7. v

An alternate arrangement avoids overlapping of the two scales by confining [the maximum angularrotation of the tool required for the .desired maximum tension to 180, by use of a stiffer spring 23. An arrangement ofthe last mentioned type. is shown in Fig. land comprises two scales increasing respectively in clockwise and counterclockwise directionsfroma common to a common maximum tension of, for instance, 70 pounds.

It will be understood that in any case the scalesare arranged on 'theface of the sheave 2| so as to be progressively visible through the index opening or window 33 of the head 24 as the sheave 2| is rotated relatively thereto during use of the tool.

In practice, the novel tool is used in a manner similar to the conventional stringing dowel hereinbefore referred to.

The racket to be strung is suitably supported in a convenient stringing position, for instance, by clamping its handle a in a vise b or other clamping device, with the frame 0 fiat side up as illustrated in Fig. 9. Assuming. that the longitudinal stringing d has been completed in the same manner as described hereinafter with respect to the transverse stringing e, the one end of the transverse stringing e is secured in place in the frame 0 in the conventional manner and the transverse string f is threaded through one of the customary holes in said frame 0 and after being interwoven with the longitudinal stringing d in the usual way is passed outwardly through the companion hole at the opposite side of the racket frame 0.

The loose end portion or is then wrapped in one and a half or two turns around the sheave 2| so as to lie in the V-groove 22 thereof, in which said convolutions of string become wedged as the tension increases.

The tool is then rotated on its axis by manually twisting the handle it to wind the string 9 upon the sheave 2| to thereby bring the handle l5, or specifically the metal band 3| thereof into engagement with the racket frame 0, for instance, as shown in Figs. 9 and 10.

As the stringer continues to rotatively twist the handle IS, the string y will develop a gradually increasing tangential tension on the sheave 2 I, so that continued operation of the tool will bring about a rotation of the handle l which is opposed by the torsional spring 23. As this twisting operation proceeds the numbers of the tension scales 32 will successively pass in registry with the index opening or window 33 of the head 24, so as to be visible therethrough directly in the line of vision of the operator or stringer.

The described twisting of the tool is continued until the tension number of the scale 32 indicating the desired tension, specified by the string manufacturer for this particular string size and material, is in registry with the index window 33 and is visible therethrough. An awl h or other suitable instrument is then forced into the particular string hole on the opposite side of the string g must be operative for both-direcfrom-that on which the tool is located, as shown in Figs. 11, and 12, to thereby clamp the string in place and ,hold it under the predetermined ten sion while the tool is removedand prepared for the next step in the stringing operation. The free string 9 is then threadedv through the next set of holes of the racket frame c and again wrapped around the sheave 2| in the groove 22 thereof, after which the aforesaid operations are repeatedto draw the next transverse string 0 up to the desired tension. iAnother awl hor its equivalent is then forced into the parti-cularhole of the racket frame 0 to hold the last. named string e under said tension after which. the first awl h or other suitable instrument is removed.

. ,The racket frame 0 is preferably clamped in a suitable frame to prevent its distortion by the string tensions developed during the stringing operation. It will be understood that the aforesaid frame is constructed so as not to interfere with the operative use of the novel tool.

These operations are repeated in sequence until the stringing of the racket is completed after which the final end of the stringing is secured in place in the conventional manner.

Figs. 11 and 12 illustrates how the novel tool is used alternatively on opposite sides of the racket and operated respectively in clockwise and counter-clockwise directions to complete the stringing operation in an efficient manner with all the strings drawn positively and accurately to the predetermined tension desired.

This result is obtained with accuracy regardless of the string diameter or the materials of which the strings are made.

While the novel tool is designed primarily for stringing rackets, it is obviously capable of other uses, for instance, as a portable scale. In such case the tension would be applied to the sheave 2| by an article to be weighed, suspended from said sheave 2| by a string or the like connected with the sheave 2| in the same way as the string f. This tensional rotation of the latter would be opposed by the torsional spring 23 or its equivalent and would, for instance, bring one of the figures of the scale 32 into registry with the window 33 to indicate in pounds or other predetermined units of measurement the weight of the article.

Although the present invention has been described in conjunction with a preferred embodiment, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Thus, it is to be observed that the spring 23 may be replaced by other equivalent types of spring and that other variations in construction may be incorporated, if desired. Such variations and modifications are considered to be within the purview and scope of the claims.

I claim:

1. A tool for stringing tennis rackets and the like comprising a handle having an axial bore, a shaft extending lengthwise of said handle and projecting outwardly beyond one end thereof, said shaft being fixed in the bore of said handle, a sleeve rotatably mounted on said shaft at the outer end thereof, a sheave attached to said sleeve and located in proximity to said end of said handle and having a peripheral groove, in dicating means on the outer face of said sheave designating tensions in predetermined units of measurement, a head fixed on the outer end of said shaft in surface proximity to said sheave and provided with an index window in registry with said indicating means, and a torsion spring in-said axial bore connected respectively with said shaft and said sheave l 2. A tool for stringing tennis rackets and the like comprising a handle, a shaft extending lengthwise of said handle and outwardly beyond one end face thereof, a peripherally-grooved sheave rotatably mounted on the outwardly projecting portion of said shaft in surface proximity to said end face of said handle, indicating means on the outer face of said sheave designating tensions in predetermined units of measurement, a head fixed on the projecting end of said shaft in surface proximity to said sheave and provided with an index window in registry with said indicating means, and means for developing a tersional tension effective on said sheave.

3. A tool for stringing tennis rackets and the like comprising a handle adapted to be rotatably twisted in contact with the'racket frame being strung, a sheave rotatably mounted on said hand-leat one end thereot in axial registry with the major axis of said handle, said sheavehav ing thestri-ngto be tensioned removably wound on said sheave to develop a tangent tension thereon, means for developing a torsional tension on said sheave in opposition to said tangent tension whereby saidstring is placed under tension, tension indicating units produced on said sheave, and means cooperating with said sheave for indicating in said tension indicating units the degree of tension applied to said string.

4. The combination of a handle, a sheave rotatably mounted on said handle in externalrelation thereto and arranged to be rotatively displaced on its axis by a force applied tangentially to said sheave, a torsion spring carried by said handle effective on said sheave in opposition to said force, and indicating means combined with said sheave for indicating said rotative displacement of said sheave in predetermined units of measurement.

BENJAMIN F. MIESSNER. 

